High-speed differential point-to-point physical signaling can be used for digital communication between different modules and equipment, e.g. in spacecraft. The receiver amplifies the small differential signal conforming to any applicable differential physical signaling standard, such as LVDS, CML, VML, LVPECL, that is received from outside the module or equipment and converts said small differential signal into a single-ended CMOS signal that can be read by digital devices. Modes of link failure include, for example, single short failure (or single short link failure, single short circuit failure)—one input line is short-circuited to a fixed voltage, double short failure (or double short link failure, double short circuit failure)—both input lines are short-circuited to fixed voltages), single open failure (or single open link failure, single open circuit failure)—one input line is disconnected, and double open failure (or double open link failure, double open circuit failure)—both input lines are disconnected. Disconnection of an input line may be due to a broken connection or due to a receiver line being connected to a switched-off transmitter that is operating in cold redundancy.
Conventionally, communication link failure mitigation techniques, e.g. for LVDS, are implemented in order to prevent erroneous data from being accepted as valid data after being received. Such erroneous data may be present in case of link disconnection in which case noise or interference can be picked up. Moreover, due to a potentially large receiver gain, the receiver may start to self-oscillate in case of link disconnection. The most common link failure mitigation techniques are to (i) add hysteresis in the receiver, (ii) introduce an offset in the differential signal, or (iii) introduce a window comparator to prevent, in case of link disconnection, the amplification of noise at the receiver input and the passing of said amplified noise as real data to the module or equipment.
However, the above approaches fail to identify any or all of single or double short failures, signal distortion, interference or self-oscillating signals. In particular, each of the above approaches fails to identify single or double short failures and single open failures, as well as self oscillating signals. Moreover, the above approaches lack the ability to assess the quality of the link and do not allow for a discrimination of typical possible link failure modes.
Not being able to detect link failure and preventing erroneous data from being accepted as valid data could lead to damage or loss of the respective module or equipment. For instance, in the case of space applications, accepting erroneous data as valid data and feeding same to the digital devices controlling operation of the module or equipment of a spacecraft could result in the loss of the spacecraft.
Accordingly, there is a need for a method and an apparatus capable of reliably detecting link failure in a receiver for receiving differential voltage signals.